The present invention relates to a rust preventive coating and a method for forming the same, and more particularly to a rust preventive coating having hydrophilic properties, air permeability and drying properties, and excellent in corrosion resistance, especially when scratches are developed. The coating is obtained by coating a surface mainly composed of iron with a metal baser or better in corrosion resistance than iron, and then, coating it with a specific paint composition, followed by drying at an ordinary temperature or heat drying at a low temperature.
Conventional rust preventing methods for iron include methods of lowering the electrode potential of iron, methods of coating the surface of iron to prevent the movement of ions, and methods of coating to prevent water and oxygen from passing through to iron, for preventing the anode reaction (formation of Fe.sup.2+) and the cathode reaction (formation of OH.sup.-) occurring on the surface of iron.
Specific examples of such rust preventing methods include coating methods with metals baser or better in corrosion resistance than iron, and coating methods by other coating means. However, in the case of only the former coating with metals, problems are encountered with regard to the durability and corrosion resistance of the metal. In the case of the latter coating with other coating means, problems arise in respect to the coating of edge portions, suppression of the occurrence of pin holes, maintenance of corrosion resistance and durability at the time when scratches are developed, and pursuing excellent processability and low cost.